Microphone



S. RUBEN MICROPHONE March 20, 1934.

Filed May 6, 1931 INVENTOR SAMUEL RUBEN BY ms ATTORNEY whcydk Patented Mar. 20, 1934 UNITED STATES MICROPHONE Samuel Ruben, New Rochelle, N. Y., assignor Ruben Patents Company, New Rochelle, N. Y., a corporation of Delaware Application May 6, 1931, Serial No. 535,357

5 Claims.

This invention relates to an improvement in microphones, and more particularly it relates to a microphone employing as a contacting element a metal compound having a negative compression resistance coefficient. My present invention is an improvement upon those described in my Letters Patent 1,748,620 and in my co-pending applications bearing Serial Numbers 490,904 and 498,941, filed respectively, October 24, 1930, and November 29, 1930.

For certain uses it is desirable to have a microphone, the contact element of which has a low resistance and is capable of withstanding the application of high current densities. An object of the invention is to meet these requirements by an efiicient device, and in this achievement, it is an improvement upon those earlier inventions.

I have found that if a body composed of a hard crystalline material, such as cupric or cup-rous sulphide and cupric and cuprous selenides and tellurides, having a low specific resistance, is coated with a compression-resistance-sensitive material having a relatively high specific resistance, such as carbon, graphite, cuprous oxide and vanadium pentoxide, the sensitivity of the element is improved. With the various combinations of these materials I have conducted comprehensive tests and found that the most efficient combination is that of copper sulphide granules coated with defiocculated graphite. A contact element so composed has a low internal resistance and a high efliciency in current discharge.

For a microphone of a high degree of sensitivity and efliciency, I employ as the vibratory electrode a disc composed of mica or similar insulating material coated on one side with gold leaf. Contact ing with this coated surface are a plurality of polished copper sulphide granules coated with a thin layer of deflocculated graphite, these latter constituting the cooperating electrode. The copper sulphide granules provide the low resistance material and the thin layer of deflocculated graphite furnishes the material of higher resistance.

The vibratory electrode is preferably made by coating one side of a mica disc with a layer of quick drying varnish or other suitable viscous material, applying gold leaf which is then rolled. An insulation ring is applied to the coated surface adjacent the periphery, and contact with the opposite side of the disc is provided by extending a strip of gold leaf to that surface.

The form of the metal plate holding the granules against the vibratory electrode has a series of concentric depressions and separating walls, the granules extending over the entire area, the walls serving to prevent the granules from compacting on one side of the instrument, both electrodes being within suitable supporting and protecting members.

As sound waves are impressed, preferably through a sound directing means, upon the mica diaphragm, its movement, by compression and release varies the conductivity of the group of granules, by changing the area of the gold leaf surface contacting with the coated granules, and permits a varying flow of current through the instrument in accordance with the impressed oscillations.

Reference is made to the accompanying drawing of an embodiment of the invention, Fig. 1 representing a cross section of a microphone and Fig. 2 an elevation with a part of the device cut away.

In the drawing, 1 represents a mica diaphragm coated on one side with gold leaf which is in contact with a plurality of cupric sulphide granules 3, coated with defiocculated graphite and extending over metal plate 2, which has a terminal at 22.. The gold leaf is connected by gold leaf strip 11 with terminal 1a. Projecting from the insulating and protecting housing 5 is hard rubber horn 4. At 6 is a handle upon which the device is mounted.

While the apparatus described is employed as a microphone, it is obvious that a like arrangement of these electrodes can be used as the contact elements in an oscillator.

What I claim is:

1. A variable resistance contact element comprising granules composed of copper sulphide coated with carbon. I

2. A variable resistance contact element comprising a copper compound with an element of the sulphur group of elements, and a surface layer of carbon.

3. In a microphonic device a contact element comprising a plurality of granules composed of copper sulphide coated with a pressure-resistance-sensitive material of higher specific resistance. I

l. A variable resistance contact element comprising contacting bodies composed of a crystalline copper compound and an element of the sulphur group, having the surface coated with a material of higher specific resistance.

5. A variable resistance contact element comprising contacting bodies composed of a crystalline copper compound and an element of the sulphur group, having the surface coated with carbon.

SAMUEL RUBEN. 

